1. Field of the Invention
The present invention generally relates to a composite plated product and a method for producing the same. More specifically, the invention relates to a composite plated product which is used as a material of sliding contact parts such as switches and connectors.
2. Description of the Prior Art
Conventionally, as materials of sliding contact parts such as switches and connectors, there are used silver-plated products wherein a conductive material such as copper or a copper alloy is plated with silver in order to prevent oxidation of the conductive material due to heat in sliding processes.
However, there is a problem in that silver coatings are easily stripped by sliding since they are soft and easily wear and since they generally have a high coefficient of friction. In order to solve this problem, there is proposed a method for electroplating a conductive material with a composite material wherein graphite particles of carbon particles, such as graphite and carbon black particles, having good heat resistance, wear resistance and lubricity, are dispersed in a silver matrix, in order to improve the wear resistance of the conductive material (see, e.g., Japanese Patent Laid-Open No. 9-7445). There is also proposed a method for producing a silver coating, which contains graphite particles, by means of a plating bath to which a wetting agent suitable for the dispersion of graphite particles is added (see, e.g., Japanese Patent Unexamined Publication No. 5-505853 (National Publication of Translated Version of PCT/DE91/00241)). Moreover, there is proposed a method for coating carbon particles with a metal oxide or the like by the sol-gel method to enhance the dispersibility of the carbon particles in a composite plating bath of silver and the carbon particles to increase the quantity of carbon particles in a composite coating (see, e.g., Japanese Patent Laid-Open No. 3-253598).
However, in the methods disclosed in Japanese Patent Laid-Open No. 9-7445 and Japanese Patent Unexamined Publication No. 5-505853, since it is required to add a dispersing agent or wetting agent for dispersing carbon particles in a silver plating bath, there are some cases where a surface active agent used as the dispersing agent or the like is absorbed onto the surface of carbon particles as well as the surface of a coating, so that the dispersing agent or the like has a bad influence on the formation of the coating. In the method disclosed in Japanese Patent Laid-Open No. 3-253598, no dispersing agent is used. However, usable plating solutions are limited in accordance with the material of a coating such as a metal oxide. For example, cyanide containing plating solutions and strong acid plating solutions can not used.
Composite plated products produced by the methods disclosed in Japanese Patent Laid-Open No. 9-7445, Japanese Patent Unexamined Publication No. 5-505853 and Japanese Patent Laid-Open No. 3-253598 have a relatively high coefficient of friction, so that there is a problem in that the composite plated products can not used as the materials of long-life contacts and terminals. Therefore, it is desired to provide a composite plated product which has a larger content of carbon and a larger quantity of carbon particles on the surface thereof than those of the composite plated products produced by the conventional methods and which has a better wear resistance than that of the composite plated products produced by the conventional methods.